should not use String#<< which is defined in mruby-string-ext; use Array#join instead; ref #2239

mrbgems/mruby-enumerator/mrblib/enumerator.rb

@@ -217,14 +217,12 @@ class Enumerator
   def inspect
     return "#<#{self.class}: uninitialized>" unless @obj
 
-    args = ""
     if @args && @args.size > 0
-      args = "("
-      @args.each {|arg| args << "#{arg}, " }
-      args = args[0, args.size-2]
-      args << ")"
+      args = @args.join(", ")
+      "#<#{self.class}: #{@obj}:#{@meth}(#{args})>"
+    else
+      "#<#{self.class}: #{@obj}:#{@meth}>"
     end
-    "#<#{self.class}: #{@obj}:#{@meth}#{args}>"
   end
 
   ##